I'm not sure exactly when it occurred but Dad received a serious injury to his right eye, most likely it occurred either in the desert battle in which he was captured or whilst on the Italian cargo ship when it was torpedoed.
Whilst at Campo 65 in Southern Italy he was sent to Bari Hospital to have the injury looked at.

Later on in Germany he was examined at Breslau hospital in an eye clinic by a special medical board with a Swiss representative included , the report from that examination is below.

Apart from the obvious benefit of getting the injury seen to there was the possibility that he could have been repatriated to England.
There was a system whereby captured troops, might be repatriated if their physical condition, injuries, disabilities etc rendered them unable or unlikely to be able to return to a combat role should they be returned to their country of origin.

I have as yet been unable to fully translate the German examination document particularly the element that is written by hand.

As I understand it though, Dad was found to be blind in his right eye and poorish vision in his left.

Despite that someone determined that the injury was not sufficient for him to be repatriated. That decision is indicated on the Bescheinigung form ( below ) where a section has been struck through leaving the word 'Verneint'  =  denied.

I still find it strange that in the midst of the awful murderous mayhem and chaos of War, particularly one as vicious and widespread as WW2  that these kind of of civilised procedures operated. 
Though of course they did not apply if you fell outside of categories determined by Nazi Germany to be civilised. For captured Russian soldiers and of course Jews there was no recourse to such acts of mercy.